Connectors are known in the art for receiving a fluid stream in a first fluid-bearing conduit and then delivering the received fluid stream to a second fluid-bearing conduit. In many cases, the fluid connection is obtained by manual alignment and coupling of separate components that comprise the connector, such as by alignment and compression of a sealing device onto a tubular device while being fitted to a receiving fitting.
The sealing device on conventional connectors is typically a ferrule having a conical frustrum exterior and a through hole. The tubular device is inserted into the through hole and the tubular device/ferrule assembly is then inserted into a receiving feature which is shaped as a complementary conical frustrum. The receiving feature is referred to as the ferrule seat. The tubular device/ferrule assembly is then forced into the ferrule seat via pressure applied by a threaded fastener.
Such an approach has several disadvantages. To effect a reliable, fluid-tight seal, the leading edge of the exterior of the ferrule must be properly oriented to the ferrule seat, which occurs only if the central axes of the ferrule and ferrule seat are perfectly coincident; both the ferrule and the ferrule seat must be fabricated to be perfectly circular; the diameter of the through hole in the ferrule must be uniformly and adequately compressed to effect a seal between the surface of the through hole and the exterior surface of the column; and the exterior of the ferrule must be uniformly and adequately compressed to effect a seal between the ferrule and the interior surface of the receiver fitting.
Other problems arise when the connector and the tubular device are subject to extended periods in a variable temperature environment. For example, in gas chromatography, a connector may be employed on a tubular device in the form of a capillary column to couple a fluid stream in the column to certain devices (such as a detector) in a chromatographic apparatus. The column may be located in a convection oven wherein the temperature environment ranges from minus 70 degrees C. to 450 degrees C. Conventional connectors, when used in such an environment, are subject to expansion and contraction. Fittings within a connector are subject to cyclical deformation, resulting in cracks. As a result, the connection fails and the connector is subject to leakage. The results of such a failure include: degradation of the column via oxidation; poor quantitation due to inaccurate measurement of column flow; interference effects of air at the detector; and degradation of analytes in the fluid stream as they react with the atmosphere.
Furthermore, most connectors are difficult to install correctly, especially by operators with minimal skills and training. Even connectors that appear to be properly installed can develop a leak at installation, which is very difficult to detect; however, the subsequent analytical run will suffer from column degradation (from oxygen diffusion), and quantitation errors. The pilot depth (i.e., the depth of the exposed tip of the column in an associated receiving device such as an inlet or a detector) is important for proper operation. The operator must measure the pilot depth when the column is installed, but this measurement is difficult and subject to error. Good laboratory practice also dictates that, upon replacement or reinstallation of a column, the ferrule should be replaced. Replacement is often a difficult or tedious procedure. For example, certain components in the connector may have become seized and are difficult or impossible to remove. Furthermore, during installation of a new connector, the column tip must be threaded through a small hole in the new ferrule, and dust or particles from the new ferrule often contaminate the column tip.
One conventional approach to resolving some of the foregoing difficulties includes a practice of fabricating the ferrule from a compliant material, such as graphite. A large insertion force is then used to force the ferrule into the ferrule seat, thus causing the ferrule to conform both to the shape of the ferrule seat and to the exterior of the capillary tube. The drawback to this approach is that a high stress is induced in the ferrule by such compression. Further, a high temperature environment will often cause such ferrule material to creep or fracture, thereby creating a fluid leak.
Another approach is to use ferrules and ferrule seats that each have a small included angle; however, a problem arises in that such a ferrule/seat combination is still prone to fracture or seizure (jamming) of the ferrule in the ferrule seat. Neither the ferrule nor the ferrule/seat combination is easily replaced.
Thus, a routine column removal, replacement, or installation task becomes an expensive and time-consuming process.
Still another approach is to encapsulate the ferrule material in a rigid container to comprise a ferrule assembly; however, such a ferrule assembly, when subjected to extremes in temperature, appears to suffer from thermally-induced mechanical creep, which can cause a leak.
Another approach is to utilize a spring-loaded ferrule (see, e.g., U.S. Pat. No. 5,163,215) so as to compensate for thermally-induced mechanical creep. This approach has the potential to prevent failures that are due to creep-induced leaks. However, the conventional spring-loaded ferrule requires a high spring force to achieve an adequate seal, which necessitates the use of a large spring and various other parts to provide a spring assembly. The ferrule/seat combination is also prone to fracture or seizure of the ferrule in the ferrule seat.
There remains a practical need for a simple, reliable, and inexpensive connector for receiving a fluid stream in a first fluid-bearing conduit and delivering the fluid stream into a second fluid-bearing conduit without incurring leaks or other failures. This need is especially apparent in environments that require fast and easy installation of a capillary column to an analytical instrument without resort to the use of tools or specialized installation techniques. Further, there is a need for a simple, reliable, and inexpensive connector that facilitates removal, replacement, or re-installation of such a capillary column.